Softwoods, such as spruce, pine, fir, larch, and cedar, are often used for interior and exterior construction due to their low cost. However, softwoods are susceptible to damage from insects (e.g., termites, woodworm, marine boring worms, etc.) and fungal degradation (e.g., “brown rot” and “white rot”) that can reduce their useful service life. Residual resins can also “bleed” through and stain surface coatings on the softwoods. Additionally, under conditions of variable atmospheric or ambient humidity, softwoods are susceptible to dimensional change which in turn can result in a change in shape and size of manufactured articles. This can, for example, cause doors and windows to “stick” and, therefore, be difficult to open or close. These same dimensional changes in unmodified wood and the associated constant expansion and contraction during typical service are one of the prime causes of flaking and cracking of applied surface coatings. Some hardwoods also have similar problems.
Acetylated wood is a modified wood product most commonly manufactured from softwoods such as Radiata Pine via acetylation. Acetylation is a chemical process involving a chemical reaction between an acetylation agent, most commonly acetic anhydride, and wood under conditions of high temperature and pressure. This process esterifies a large proportion of the accessible hydroxyl groups present within the cell walls of the wood structure. The acetylated wood retains a similar lignin content as before treatment, which allows the acetylated wood to maintain structural rigidity. However, in contrast to softwood before acetylation, acetylated wood is more resistant to dimensional change when subjected to variable environmental humidity and temperature which means reduced expansion, contraction and warping. This improved dimensional stability not only reduces the likelihood of sticking or excessively loose windows and doors but can also improve the service life of applied external coatings. Additionally, compared to softwoods in their natural untreated state, acetylated wood is inherently more resistant to attack by insects and to fungal degradation, allowing for it to be used for exterior construction without the need for additional preservation treatments or coatings. Moreover, the Radiata Pine and many other softwoods which can be used to produce acetylated wood are fast-growing and can be harvested sustainably.
However, acetylated softwoods can lack the visually aesthetic qualities of hardwoods. For example, acetylated softwood is usually pale in color and can become even paler as it ages and is exposed to natural weathering. The surface of acetylated wood can also be spoiled by the appearance of surface mold and other discolorations. By contrast, hardwoods tend to hide blemishes better by virtue of their aesthetically more pleasing and, usually, darker color.